1. Field of the Invention
The present invention relates to a testing method of a semiconductor integrated circuit and testing equipment, and in particular, to a method for testing a deviation amount and a period of a frequency in a semiconductor integrated circuit, the method having the steps of minutely deviating a frequency of a clock signal used as a reference and outputting a signal where peaks of a frequency spectrum are dispersed, and equipment thereof.
2. Related Background Art
FIG. 3 is a block diagram for explaining a method of testing for a deviation amount of a frequency in conventional testing equipment for a semiconductor integrated circuit, which comprises a reference clock generator 11, a target IC 12, and a spectrum analyzer 13. When a reference clock is inputted into the target IC 12 from the reference clock generator 11, the reference clock is outputted from the target IC 12 as a signal having a frequency deviated in a certain spectral bandwidth. A frequency spectrum of this output is analyzed with the spectrum analyzer 13, and the deviation amount of the frequency is tested for.
However, there are the following issues in the conventional testing method of a semiconductor integrated circuit that is described above.
(1) An expensive spectrum analyzer is needed.
(2) Displaying the whole deviation of a frequency takes much time.
(3) When performing spectrum analysis of a pulse waveform, it is hard to obtain a spectrum having a form with clear edges.
(4) When the deviation amount of a frequency is small, a spectrum analyzer with fine frequency resolution is needed.
(5) A period of the deviation of a frequency cannot be tested for in the spectrum analyzer.
Accordingly, an object of the present invention is to provide a testing method of a semiconductor integrated circuit and equipment thereof which make it possible to test for the deviation amount of a frequency without using expensive equipment such as a spectrum analyzer.
In addition, another object of the present invention is to provide a testing method of a semiconductor integrated circuit and equipment thereof that make it possible to test for a period of the deviation of a frequency.
According to one aspect, the present invention which achieves these objectives relates to a testing method of a semiconductor integrated circuit comprising the steps of inputting a reference clock signal into a semiconductor integrated circuit to be tested, making a signal, obtained by minutely deviating a frequency, outputted, subtracting a signal having the same period as the reference clock signal from the above-described signal outputted, accumulating the result of subtraction every fixed time, and computing the deviation amount of a frequency on the basis of an amplitude of a waveform obtained from the result of accumulation.
According to another aspect, the present invention which achieves these objectives relates to testing equipment of a semiconductor integrated circuit comprising input means for inputting a reference clock signal into a semiconductor integrated circuit to be tested, subtracting means for subtracting a signal having the same period as the reference clock signal from the signal that is outputted from the above-described semiconductor integrated circuit and is obtained by minutely deviating the frequency of the reference clock signal, adding means for accumulating the output of the above-described subtracting means every fixed time, and computing means for computing the deviation amount of a frequency on the basis of the amplitude of a waveform obtained from the result of accumulation every fixed time.
Other objectives and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.